validation error caused by validateOnBlur after array field is deleted

[shrugs]

when following validateOnBlur, mobx-react-form attempts to validate a field on blur using a debounce, but if the parent field is deleted before this debounce timeout expires, the validator attempts to invalidate a non-existent field, causing a (Error): Validation Error: Invalid Field Instance

This occurs when:

1. focus an input for a parentField's nested field
2. click the remove button (which calls parentField.onDel)
3. wait a few ms for the debouncer
4. Invalid Field Instance thrown because, indeed, the field instance no longer exists

---

A (horrible) workaround at the moment is to simply delay the removal of the field until after validation has occurred.

_remove = () => {
    setTimeout(() => {
      this.props.field.del()
    }, 251) // default validationDebounceWait is 250ms
  }

[shrugs]

I was unable to disable validation just-in-time because the debounce is scheduled immediately after the input is defocused, and before the event to remove the field is received, so there's no way to cancel it.

One option would be to disable validateOnBlur altogether and implement it ourselves, only calling the validate function if the removal event was not called within some duration.

[shrugs]

I was able to obscure the removal delay by using some nice css transitions, so this isn't realistically the worst thing in the world anymore.

[foxhound87]

Related to:
#371
#399